from __future__ import annotations

import hashlib
import json
from datetime import datetime
from typing import List

from .models import PlanDelta


class GovernanceLedger:
    def __init__(self) -> None:
        self.chain: List[dict] = []  # each entry: {index, hash, prev_hash, delta, ts}

    def _hash_entry(self, prev_hash: str, entry: dict) -> str:
        data = json.dumps({"prev_hash": prev_hash, "entry": entry}, sort_keys=True)
        return hashlib.sha256(data.encode("utf-8")).hexdigest()

    def append(self, delta: PlanDelta) -> str:
        prev_hash = self.chain[-1]["hash"] if self.chain else "0" * 64
        entry = {
            "version": delta.version,
            "plan": delta.plan,
            "provenance": delta.provenance,
            "signature": delta.signature,
            "ts": datetime.utcnow().isoformat() + "Z",
        }
        entry_hash = self._hash_entry(prev_hash, entry)
        self.chain.append({"index": len(self.chain), "hash": entry_hash, "prev_hash": prev_hash, "entry": entry})
        return entry_hash

    def root(self) -> str:
        if not self.chain:
            return "0" * 64
        return self.chain[-1]["hash"]

    def attest(self, delta: PlanDelta, key: str = "ledger") -> str:
        # Lightweight attest placeholder
        payload = delta.to_json()
        return hashlib.sha256((payload + "::" + key).encode("utf-8")).hexdigest()